This invention relates to a container having an opening, or mouth, covered with a flexible sheet of material, and an outer closure lid disposed above the flexible sheet. Such containers are generally used in the food packaging industry and embody various sizes, shapes and forms for packaging various food products, particularly of the flowable type.
Cottage cheese, butter, yogurt and similar foot-stuffs are commonly packaged and marketed in a container that is generally wax-coated or wax-impregnated paper or plastic. The container has a receptacle portion, consisting of a base and upwardly extending sidewall, and an outer closure lid which is pressed onto the sidewall top peripheral opening, or mouth, as snuggly as possible so as to minimize the entry of air or the escape of food-stuff from the closed container. Outer closure lids for such containers are either the plain disc-like lids which engage a peripherally extending bead located below the mouth rim on the container on the interior surface of the sidewalls, or so-called flush-type lids which fit across the opening of the container and have a depending skirt or snap-on engagement with an exterior portion of a beaded rim of the container, or so-called plug-type lids which project into the interior of the container adjacent the inner surface of the upwardly extending sidewall and engage the sidewall opening in snap-on relation.
Conventionally, with containers of this type, it is relatively easy for the consumer, or other person, to remove the outer lid as well as the underlying flexible sheet closure. Because of the relative ease with which the flexible sheet closure and the outer closure lid may be removed from the top of the container, innocent, or willful and malicious tampering with the container's internal contents is possible. After removing the outer lid closure, a potential consumer may lift up a portion of the flexible sheet closure from engagement with the top of the container. With such containers, it is possible to determine if the flexible sheet closure has been loosened from the top of the container, but only by lifting the outer closure lid from the container and performing a close inspection.
In known containers which include a flexible sheet inner closure underneath the lid, such as those disclosed in U.S. Pat. Nos. 3,301,464; 3,338,027 and 3,471,992, a thin film or sheet of flexible material is disposed across the opening of the top of the container and is in contact with, and supported by, the top peripheral surfaces of the rim of the container. With those containers employing plug-type lids, the plug-type lid presents a substantially vertical and peripherally-extending wall area, which will lie adjacent to the interior surface of the container sidewall immediately below the top edge of the rim of the container when the lid is placed thereon. This vertically disposed peripheral wall area of the plug-type lid will engage a portion of the flexible sheet film and press it against the interior surface of the sidewall of the container. In some conventional containers, the flexible sheet closure is heat-sealed to the portion of the container sidewall adjacent the vertical and peripherally-extending wall area of the plug-type lid. In other containers, the flexible sheet closure material may be heat-sealed across the upper surface of the rim of the container. Further, instead of heat-sealing, adhesive means can be employed.
While such double-seal containers have functioned generally satisfactorily, several problems have been encountered, both in manufacture and in ultimate use. With respect to manufacturing, in accordance with known techniques, it is necessary to cut the sheet closure to a relatively precise size and shape corresponding to the size and shape of the container lid and the mouth of the container. And, it is necessary to maintain the sheet in relatively precise registry with the lid and to secure the sheet to the lid prior to insertion of the lid into the mouth of the container. The strength of the attachment between the lid and sheet must be accurately controlled to prevent the lid from tearing the sheet when the lid is removed, as for example, to check the tamper-proof integrity of the container. And, since the sheet does conform in size and shape to the lid and mouth of the container, there are no readily graspable tabs to facilitate removal of the sheet when it is desired to get access to the contents of the container.
Owing to the possibility and ease of opening of the flexible sheet closure, as a result of inadvertent shipping and handling activities or as a result of innocent potential consumer curiosity or malicious tampering, it is desirable to be able to more easily determine if the flexible sheet closure has been opened. Further, it is desirable that a tamper-indicating construction be employed with such flexible sheet closures that will allow the closure to be used with many types of lids and containers now in use. Advantageously, such a tamper-indicating construction of a flexible sheet closure should be effective regardless of the manner of engagement of the closure with the upper rim of the container. That is, the tamper-indicating flexible sheet closure construction should be effective regardless of whether or not the flexible sheet closure is heat-sealed or adhesively secured to the top rim of the container or just non-sealingly supported thereon. Further, it is desirable that the tamper-indicating construction of the flexible sheet closure not require visual inspection through complicated, relatively more expensive, transparent windows in the outer closure lid when such outer closure lid is used. The taper-indicating flexible sheet closure construction should also work with a large variety of different types of flexible sheet materials that may be used.